91 b250 van running too rich

Hello
I am new to this forum i have a 91 dodge b250 van with a 318 and throttle body injection abt a week or so ago i noticed it started getting really bad fuel milage and i am noticing there is black smoke coming from the exhaust when im idleing at a light in gear and its worse with the a/c on and when im driving it seems like there is no power unless i floor it and the trans kicks down then it clears out and runs I pulled the trouble codes from the ecm as yes it has turned on the check engine light the codes are as follows
12, 51, 51, 32, 55 i am changing the air filter as it was dirty and someone told me to try changing the coolant temp sensor for the ecm as it may think the engine is cold

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Level III Supporter

Welcome to Allpar. To begin with, I would not change any parts until you can diagnose this a bit to first find out what parts you may actually need. It will save you time, money and frustration. Don't guess and throw parts at it. You can follow basic fault code interpretations here:http://www.allpar.com/fix/codes/index.html
You still might want to get a good (factory) service manual with wiring diagrams and diagnostic service procedures. I don't know your skill sets or tool inventory.
It appears to be running rich (code 51), you may want to start by measuring fuel pressure at the throttle body.
How are the cap, rotor, wires and plugs? Are the spark plug tips black with carbon fouling? This may cause them to misfire. Then raw oxygen going past the O2 sensor will make the PCM think that it is running lean. It will then drive the injectors rich. This will exacerbate the situation with fouled spark plugs and keep them fouled.
You want the correct Champion type Copper Plus called for on the underhood emissions label.
Is gasoline dripping from the injectors at idle? There should be a light gas spray at idle from the injectors.
Fault code 32 is odd if the 'ck eng' (service engine soon) light is working.
Sometimes the coolant sensor wiring and terminal could corrode. There are 2 separate sensors, one for the dash gauge and one for the computer. The dash gauge sensor is the Violet wire, You want to look at the other one (Bk w/stripe?). Many times, this condition would not set a fault code.

Level 2 Supporter

Code 32 is EGR and code 51 is O2 sensor.
Before replacing either, check the ground lug and carefully check the wire crimped into it, at the driver's side rear corner of the block. That's the ground for these sensors, and that wire often frays or breaks. Even if it looks OK, remove and clean the whole connection. Then check the entire harness on the backside of the valve cover for frayed or baked wires.

Thanks fellas for the replys In have been around cars and building cars since i was 16 (60) now I have built many drag cars and dirt track cars but im a carburetor man and fuel injection even the old throttle bodies are all pretty new to me still as far as trouble shooting and repairing them so hopefully this old dog can learn a few new tricks i did change the temp sensor today and that was not the problem and put in new air filter. Van hadnt been tuned up in abt 5 yrs i had a company truck for yrs but lately i have been using the van as a work commuter so it wont hurt to replace cap rotor and plugs as im sure plugs are black cap and rotor had some corrosion on the contacts Will also check the ground wiring and all wire harness as Bob mentioned for any shorting i finally found the o2 sensor im going to check the wire harness to it tomorrow as it looks like it could be up against the frame it may have rubbed thru and could be shorting out i will check these things out tomorrow let yall know if it solves anything
Thanks again for the ideas

Ok so i changed plugs an capand rotor cleaned and checked the ground on back of engine checked for worn spots on any harness could find none still throwing 51, 51 and a 32 code i have no idea when or if the O2 sensor has ever been changed any more suggestions ?? should i look into changing the o2 sensor?

Level 2 Supporter

With both of those codes, I'd look at the EGR first, since if it malfunctions, it can induce a fault code for an O2 sensor. Rev the engine and see if the stem of the EGR valve moves. If it doesn't, replace it. Also, lift the stem with engine at idle and see if the engine stumbles or stalls - it should. If it doesn't, the EGR passage may be clogged.

Level III Supporter

I have also had EGR valves where the stem behaved normally, but the tip of the valve (pintle) had burned off.
You could blow through the valve with it off the vehicle. You shouldn't be able to do that with the vacuum hose off.
It was getting EGR all the time.

I checked egr all seem to be fine with it i was checking the fuel pressure regulator to see if it had a bad diaphram i applied some vacuum and when i did the black smoke from the tail pipe stopped and the engine seemed to smooth out when i released pressure it started to push black smoke again so i put a vac gauge on the port of the throttle body where the fuel press reg vac hose hooks to on the throttle body and i have no vac signal at any throttle position. Is a this supposed to be ported or manifold vac at this port?? I m thinking the passage way may be clogged not getting any vac to the reg. What do you fellas think??? Im going to pull throttle body this weekend and clean it to see if that makes a difference. When should i be getting a vac signal at the regulator??
Thanks

Thanks fellas that's what i thought it was manifold vac the hose to the reg is short abt 2" i connected the vac gauge directly to the TB port and had no vac at any engine rpm i will remove the TBI this weekend and give it a good cleaning i suspect carbon blockage as well and i will replace any vac hoses i encounter also